In recent years computed radiography (CR) systems have been successful in replacing analog screen/film (SF) in many clinical settings. Such CR systems use photostimulable x-ray storage phosphor plates (for example, BaFBr:Eu2+), which are exposed in cassettes and then brought to an automated plate scanner, to read out the stored image information.
CR systems bring numerous advantages such as electronic transmission and storage, image processing, and computer-aided diagnosis to clinical departments, in a practical and highly affordable way. However, technical progress in the CR field has reached a plateau (perhaps in part because of economic developments at the chemical imaging companies who originally supported the development of the technology), and CR image quality performance has been surpassed by flat-panel based digital radiography (DR) systems.
DR systems, however, are much more expensive than CR, which has limited their clinical acceptance. A single CR reader can support multiple cassettes and replacing the SF cassettes with CR cassettes can retrofit an entire radiology department. Each individual detector in a room requires a separate DR detector. Furthermore, the replacement cost for a worn out or broken DR detector can be ten to one hundred times more expensive than replacing a CR cassette.
The image quality performance of CR has been limited in the past by three factors: (1) When the CR screen is made thick enough to achieve good x-ray absorption, the spatial resolution is disadvantaged compared to SF or DR, a particular problem for applications like mammography or bone radiography, (2) Because of limitations in screen conversion gain, collection efficiency, and detection efficiency, in a CR system that is not optimally designed, the number of detected electrons per absorbed x-ray (“gain”) can become low enough to become a secondary quantum sink, (3) CR systems have been observed to have rather high gain fluctuation noise, or “Swank noise”, compared to high quality SF or DR systems.
The proposed novel CR detector system is significant because it removes the above-mentioned image quality limitations at an affordable cost. A CR system based on novel transparent storage phosphor (TSP) materials and improved scanner apparatus provides image quality equal to or better than DR, in particular for the high-resolution application of mammography.